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Abstract:

Metamaterials or artificial negative index materials (NIMs) have
generated great attention due to their unique and exotic electromagnetic
properties. One exemplary negative dielectric constant material, which is
an essential key for creating the NIMs, was developed by doping ions into
a polymer, a protonated poly(benzimidazole) (PBI). The doped PBI showed a
negative dielectric constant at megahertz (MHz) frequencies due to its
reduced plasma frequency and an induction effect. The magnitude of the
negative dielectric constant and the resonance frequency were tunable by
doping concentration. The highly doped FBI showed larger absolute
magnitude of negative dielectric constant at just above its resonance
frequency than the less doped PBI.

3. The method of claim 2, wherein the dielectric material comprises a
polymer and wherein doping ions into the polymer further comprises:
immersing the polymer into an acid solution for a predetermined period of
time at a predetermined temperature; removing the doped polymer from the
acid solution; drying the doped polymer; and heating the doped polymer
for a predetermined period of time at a predetermined temperature.

6. The method of claim 5, wherein the phosphoric acid solution has a
predefined concentration from about 0.001 wt % to about 90 wt %.

7. The method of claim 3, wherein immersing the polymer into an aqueous
acid solution for a predetermined period of time at a predetermined
temperature comprises immersing the conductive polymer into an aqueous
acid solution for a time of about 1 second to about 480 hours at a
temperature of about -20.degree. C. to 80.degree. C.

8. The method of claim 3, wherein heating the doped polymer for a
predetermined period of time at a predetermined temperature comprises
heating the conductive polymer for a time of about 1 second to about 480
hours at a temperature of about room temperature to about 110.degree. C.

14. The negative dielectric material of claim 11, wherein the ion
comprises phosphate and wherein a concentration of phosphate in the
poly(benzimidazole) is about 0.001 wt % to 90 wt %.

15. The negative dielectric material of claim 10, wherein a plasma
frequency and an effective dielectric constant of the material are
controlled by concentration and effective mass of dopant ions and by
operating temperature.

16. The negative dielectric material of claim 15, wherein the material is
characterized with an optical property that is tailored by controlling a
plasma frequency.

17. The negative dielectric material of claim 9, wherein a resonance type
of conductivity of the material is controlled by concentration and
effective mass of dopant ions and by operating temperature.

22. The microwave device of claim 21, wherein the microwave device is
characterized as an antenna, a filter, or a cloaking device.

Description:

[0001] Pursuant to 35 U.S.C. §119, the benefit of priority from
provisional application 61/256,577, with a filing date of Oct. 30, 2009,
is claimed for this non-provisional application, the contents of which
are incorporated herein by reference thereto.

[0004] Metamaterials or artificial Negative Index Materials (NIM) are a
new class of electromagnetic materials or structures that have generated
great attention over the last ten years due to their unique and exotic
electromagnetic properties. They are constructed with specially designed
inclusions and architecture in order to exhibit a negative index of
refraction, which is a property not found in any known naturally
occurring material. These artificially configured composites have a
potential to fill voids in the electromagnetic spectrum where
conventional material cannot access a response, and enable the
construction of novel devices such as microwave circuits and antenna
components. The negative effective dielectric constant is a very
important key for creating materials with a negative refractive index.

[0005] To achieve a negative dielectric constant, two main approaches have
been employed in the art. One approach involves the use of a periodic
structure whose frequency spectrum mimics the response of a high pass
filter or a waveguiding structure--for example a hollow metallic
waveguide loaded with periodic split ring resonators. Under this
condition, electromagnetic waves are evanescent at low frequencies and
this evanescence in the small frequency gap is described in terms of
negative permittivity values below some specific frequency (i.e., the
corner (or cutoff) frequency). The second approach involves the use of a
composite comprising of metal inclusions in a dielectric matrix. It has
been verified experimentally on a micrometer level that the effective
dielectric constant of a composite containing conducting micro-fibers
(diameter ˜25 μm) was negative at GHz frequencies. It has also
been proposed that a composite that consists of short ferromagnetic wires
embedded into a dielectric matrix, can exhibit a tunable effective
negative dielectric constant under a DC magnetic field.

[0006] The first approach in the art involves assembling periodic
geometrical structures made up of inductors and capacitors on a
micrometer scale, which is extremely difficult and not readily applicable
for producing commercial metamaterials with conventional materials. The
second approach in the art of using metal inclusions is not desirable
because of the difficulty in making a homogenous material without
aggregation. The limitation of tunability of the resonance frequency is
another big problem with the two approaches, since the resonance
frequency can be tuned only by dimensional change of the components in
these systems. Accordingly, new ways of manufacturing materials, and
materials themselves, are being continuously sought.

BRIEF SUMMARY

[0007] One object of the invention is to provide Metamaterials or
artificial negative index materials (NIMs) having unique and exotic
electromagnetic properties. In one embodiment, negative dielectric
constant materials, which are essential keys for creating the NIMs, have
been developed by doping ions into polymers, such as with a protonated
poly(benzimidazole) (PBI). Such exemplary doped PBI shows a negative
dielectric constant at megahertz (MHz) frequencies due to its reduced
plasma frequency and an induction effect. The magnitude of the negative
dielectric constant and the resonance frequency were tunable by doping
concentration. Highly doped PBI showed larger absolute magnitude of
negative dielectric constant and lower resonance frequency at just above
its resonance frequency than the less doped PBI.

[0008] In another embodiment of the invention, a method of manufacturing
an effectively homogeneous negative dielectric material comprises
providing a dielectric material, doping ions into the dielectric
material, and recovering an effectively homogeneous negative dielectric
material. The dielectric material may comprise dielectric ceramics,
polymers or composites thereof.

[0009] In yet another embodiment, wherein the dielectric material
comprises a polymer, the step of doping ions into the polymer can
include: (1) immersing the polymer into an acid solution for a
predetermined period of time at a predetermined temperature; (2) removing
the doped polymer from the acid solution; (3) drying the doped polymer;
and (4) heating the doped polymer for a predetermined period of time at a
predetermined temperature. One preferred polymer includes
poly(benzimidazole). One preferred acid solution includes an aqueous
phosphoric acid solution. Such phosphoric acid solution has a predefined
concentration range, such as from about 0.001 wt % to about 90 wt %. The
polymer can be immersed into the aqueous acid solution for a time of
about 1 second to about 480 hours at a temperature range of about
-20° C. to about 80° C. The polymer may be heated for a
time of about 1 second to about 480 hours at a temperature range of about
room temperature to about 110° C.

[0010] In addition to the method of manufacturing a negative dielectric
material, as described above, still other aspects of the present
invention are directed to corresponding negative dielectric materials
themselves.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0011] Having thus described the invention in general terms, reference
will now be made to the accompanying drawings, which are not necessarily
drawn to scale, and wherein:

[0012] FIG. 1 illustrates the synthesis of phosphoric acid doped
poly(benzimidazole), in accordance with embodiments of the present
invention;

[0013] FIGS. 2A and 2B illustrate the dielectric constant of PBI doped
with 50 wt % of H3PO4 aqueous solution as functions of
frequency and temperature (FIG. 2A) and a 3-D plot of minimum dielectric
constant, temperature and frequency (FIG. 2B); and

[0015] Embodiments of the invention include negative dielectric materials
and methods of manufacturing negative dielectric materials. A negative
dielectric constant material was developed by doping ions into
poly(benzimidazole) (FBI). The doped PBI showed a negative dielectric
constant at megahertz (MHz) frequencies due to its reduced plasma
frequency and an induction effect. The magnitude of the negative
dielectric constant and the resonance frequency were tunable by doping
concentration. The highly doped PBI showed larger absolute magnitude of
negative dielectric constant and lower resonance frequency at just above
its resonance frequency than the less doped PBI. Specifically, the FBI
doped with 60 wt % phosphoric acid solution showed a very large absolute
magnitude of negative dielectric constant of -7.35×104 at
300° C. and 8.28×104 Hz and the PBI doped with 50 wt %
phosphoric acid solution showed a smaller absolute magnitude of negative
dielectric constant of -1.39×104 at 300° C. and higher
frequency 1×105 Hz. As temperature increased, the dielectric
behavior changed from a relaxation spectrum to a resonance spectrum
showing larger magnitude of negative dielectric constant at a lower
frequency. The conductivity of the doped PBI measured as a function of
both temperature and frequency followed the same trend as the dielectric
constant. With respect to the dielectric constant and the conductivity
data, the origin of the negative dielectric constant was attributed to
the resonance behavior of the high mobility of ions at elevated
temperatures and high frequencies. The utilization of the developed
negative dielectric material thus provides novel approaches for making
unique optical and microwave devices such as filters and switches.

[0016] Without wishing to be bound by any one theory, one aspect of the
invention involves doping high mass charge carriers into materials to
make homogenous negative dielectric materials with reduced plasma
frequencies (ω.sub.ρ). It is well known that below the plasma
frequency, ω.sub.ρ, the dielectric constant of a conductive
metal is negative. For example, the dielectric constant of aluminum is
negative below its high plasma frequency, ω.sub.ρof 15 eV
(3.63×1015 Hz), with the small mass of charge carriers,
electrons (mc ˜9.11×10-31 kg). However, if the
effective mass of charge carrier increases, the plasma frequency can be
lowered. For example, if the charge carriers are mainly heavy ions, the
ions oscillate under an electric field at their ionic plasma frequency
(ω.sub.ρ*) given by
ω.sub.ρ*≈ω.sub.ρ(me/mi)0.5,
where me is the effective mass of electron and mi is the
effective mass of ion. Thus, the ions oscillate much lower plasma
frequencies than the electrons. In general, the material doped with ions
is very homogeneous at the molecular level in contrast to other
multiphase composites with metallic inclusions. The induction of highly
conductive dopants (ions or nano-scale inclusions) of the material can
influence the resonance spectrum, which is another synergetic benefit for
making negative dielectric constant material at a lower frequency. The
value of negative dielectric constant and the resonance frequency can be
tuned as a function of dopant concentration and the use temperature.
Based on this principle, one exemplary negative dielectric material was
developed with ion doped conducting polymers and a phosphoric acid doped
poly(benzimidazole).

[0017] Poly(benzimidazole) (FBI) was prepared using a modification of
previously reported synthesis methods. The general process of the
solution polycondensation reaction began with Poly(phosphoric acid) (PPA)
being added to a 250 ml three-necked flask equipped with a mechanical
stirrer, a nitrogen inlet and outlet. The flask was immersed in an oil
bath and stirred at 80° C. for several hours to remove residual
air from the flask. The temperature of the PPA was taken to 140°
C. and a stoichiometric ratio mixture of 3,3'-diaminobenzidine (DAB) and
isophthalic acid (IPA) was charged into the flask under nitrogen flow
while stirring. The reaction mixture was vigorously stirred at
140° C. for 5 hours and 200° C. for 18 hours. The hot
slurry solution was poured into water for precipitation and the
precipitated polymer was immersed in a 5 wt % Na2CO3 aqueous
solution for at least 24 hours. The polymer was obtained by vacuum
filtration, washed with deionized water, and dried in a vacuum oven at
110° C. overnight.

[0018] The PBI films were prepared from 5% (w/v) solutions in
N,N'-dimethylacetamide (DMAc). The filtered polymer solutions in DMAc
were heated with vigorous stirring for several hours to facilitate
dissolution of PBI. The polymer solutions were poured onto glass plates
and were placed in a dry box for 48 hours to form membranes. The
membranes were oven dried at 100° C. for 1 hr and 200° C.
for 1 hr. The films were isolated from the glass plates in cold water.
The PBI membrane was then dried at 100° C. for 24 hours under
vacuum. The acid-doped PBI film was obtained by immersing the membrane in
various concentrations of aqueous phosphoric acid (i.e. 50 or 60 wt %)
solution for 48 hours at room temperature. The doped polymer membrane was
blot dried with a paper towel and placed in an oven at 40° C. for
24-48 hours under vacuum. After the membrane was dried, it was weighed to
determine the amount of phosphoric acid uptake. The doping level of the
membranes was determined by the concentration of phosphoric acid, with
the doping level of a PBI membrane immersed into a 60 wt % phosphoric
acid solution for 48 hours being as high as five phosphoric acid
molecules per repeat unit. A summary synthesis scheme of phosphoric acid
doped FBI is illustrated in FIG. 1.

[0019] The infrared (IR) spectra of pure PBI and doped PBI were measured.
The interactions between PBI membranes and phosphoric acid were
extensively studied by Infrared Spectroscopy. For PSI, a broad peak
corresponding to the free N--H stretch and the self-associated, hydrogen
bonded N--H groups were observed in the spectral region 4000-2500
cm-1. The absence of a carbonyl peak in the spectral region
1540-1870 cm-1 confirmed ring closure. Also, the C═C and C═N
stretching vibrations were observed at 1606 cm-1, in-plane
heterocyclic ring vibrations were observed at 1444 cm-1, a breathing
imidazole ring stretch was observed at 1287 cm-1, and a strong
absorption for out of plane C--H bending for benzene rings was observed
at 799 cm-1, All of which were conclusive for benzimidazoles. For
the H3PO4 doped FBI films, we confirmed that the IR spectrum of
the PBI was greatly modified after protonation and complexation with
phosphoric acid. A broad and intense band in the 2000-3500 cm-1 was
the result of the presence of protonated PBI, the complexation with
phosphoric acid, and the existence of strong hydrogen bonding.
H3PO4 protonated benzimidazole rings, resulting in the
formation of anions. Absorption bands in the 500-1300 cm-1 spectral
region were characteristic of anions. H2PO4- was the
predominant anion in the entire concentration range. The H2PO4-
anions in the membrane play a dominant role in the proton conductivity
because they contain both proton acceptor and donor sites, allowing them
to contribute to the overall proton transport in the system. The anions
of phosphoric acid were believed to be immobilized and held by the PBI
matrix by strong hydrogen bonding thus forming an effective network for
proton transport.

[0020] A series of dielectric spectra of the 50% doped PBI at various
temperatures as a function of frequency has been determined and is shown
in FIG. 2A. The dielectric constant decreased with increasing frequency.
When the sample was measured at 25° C., the dielectric constant
was 118 at 10 Hz and decreased to 7.65 at 1×106 Hz. When the
dielectric constant was measured at elevated temperatures, the dielectric
constant increased with increasing temperature. The dielectric constant
measured at 10 Hz and 300° C. was 5 orders of magnitude higher
than that measured at 10 Hz and 25° C. Most interestingly, the
dielectric constant resonance spectrum appeared in the range of
1×105 Hz and 1×106 Hz. It exhibited a transition
from positive to negative value, reaching a minimum at around
1×105 Hz.

[0021] The increase in the dielectric constant at a low frequency was
indicative of the presence of interfacial polarization. This led to field
distortion and gave rise to induced dipole moments. This effect was
prevalent at low frequencies since the dipole relaxation time of this
type of polarization was large. In the example system, there was an
abundance of mobile ions present, which resulted in significant
interfacial polarization. Without wishing to be bound by any one theory,
the increase of the dielectric constant at low frequencies with
increasing temperatures is believed to be explained by the higher
polarization resulting from the higher mobility of doped ions.

[0022] In order to understand the dielectric constant resonance behavior,
the minimum dielectric constant and the frequency at the minimum
(fmin), just above resonance frequency (fres), were recorded at
each temperature as shown in FIG. 2B. The minimum dielectric constant
slightly increased from 7.65 to 19.1 over the temperature range of 25 to
120° C. Above 130° C., the minimum dielectric constant
began to decrease gradually and reached a negative value of -124 at a
temperature of 160° C. Above 160° C., the minimum
dielectric constant decreased steeply and reached -1.39×104 at
a temperature of 300° C. Over the temperature range of 25 to
150° C., the dielectric constant kept decreasing with increasing
frequency and the fmin frequency remained constant because no
fmin frequency appeared up to 1.53×106 Hz, which was the
highest measuring frequency limit. As the temperature increased above
160° C., the fmin frequency decreased drastically because the
mobility of the ionic charge carriers increased with increasing
temperature. However, above 230° C., the fmin frequency
remained constant with increasing temperature. Above 4×105 Hz,
the minimum dielectric constant was relatively insensitive to the
frequency. Below 4×105 Hz, however, the dielectric constant
dropped dramatically over a very small frequency interval due to
increased contribution of the sluggish ionic charge carriers.

[0023] The conductivity of the doped PBI was also measured as a function
of frequency and temperature. The effects of frequency and temperature on
the conductivity were very similar to those observed in the dielectric
constant measurements. The overall conductivity increased with increasing
temperature, reaching a maximum at a frequency between
1×105-1×106 Hz. The conductivity measured at 10 Hz
at a temperature of 300° C. was three orders of magnitude higher
than that measured at 10 Hz at a temperature of 25° C. (FIG.
3(a)). Above 160° C., the conductivity increased very rapidly with
temperature and displayed a peak at a frequency of
˜1×105 Hz. This was fairly close to the frequency at
which the dielectric constant reached its most negative value.

[0024] The maximum conductivity as a function of frequency (fmax) was
recorded at each temperature. The maximum conductivity slightly increased
over the temperature range of 25 to 120° C. At 130° C., the
maximum conductivity began to decrease gradually, and above 160°
C., it increased steeply and reached 4.90×10-3 S/cm at a
temperature of 300° C., showing a plateau. The discontinuous
transition was at 160° C. Below 150° C., the frequency
(fmax) of maximum conductivity was insensitive to increasing
temperature. Above 160° C., however, the frequency (fmax) of
maximum conductivities dropped dramatically, plateauing at about
1×105 Hz. Above 4×105 Hz, the maximum conductivity
was relatively insensitive to the frequency. Below 4×105 Hz,
however, the maximum conductivity increased dramatically with decreasing
frequency over a very small frequency interval.

[0025] Without wishing to be bound to any one theory, it is believed that
the temperature dependence of the conductivity is due to the mobility of
ions in the inventors' materials. Above 160° C., the mobility of
ions began to increase because of the increased mobility of the chain
segments of PBI at that temperature. The temperature dependence of the
dielectric and conductivity data suggested a glass transition temperature
of about 160° C. This was consistent with a glass transition
temperature of about 170° C. measured by a dynamic mechanical
analyzer.

[0026] Without wishing to be bound by any one theory with respect to the
dielectric constant and the conductivity data, it is believed that the
origin of negative dielectric constant with the resonance behavior is
attributed to the mobility of ions of the doped PBI at elevated
temperatures. Accordingly, this effect of mobility of ions on dielectric
constant can be explained by two approaches: a microscopic approach
explained by ionic plasma resonation and a macroscopic approach explained
by an induction effect.

[0027] For the microscopic approach to explain the negative dielectric
behavior, the plasma frequency, ω.sub.ρof the doped PBI can be
considered. The ions oscillation under an electric field at lower plasma
frequency ω.sub.ρ*) than a normal electron oscillation, given
by ω.sub.ρ≈ω.sub.ρ(me/mi)0.5.
Furthermore, both the interaction between electrons and ions and the
lower density of charge can reduce the ion oscillation frequency. For the
macroscopic approach, the induction effect on the negative dielectric
constant was known to exist in a composite comprised of conductive
rod-fillers in a dielectric matrix. The dispersion of the effective
dielectric constant can range from a relaxation type to a resonance one,
depending on the conductivity of the inclusion and their dimension. It
has been reported that low conductivity inclusions influence the
relaxation spectrum and high conductivity inclusions influenced the
resonance spectrum at a high frequency. Conductive thin rods interact
with an external field like dipoles and the skin effect increased with
increasing frequency. In embodiments of the invention, at temperatures
below 160° C., the conductivity was not high enough, so the
material displayed a dielectric relaxation type spectrum. Above
160° C., however, the conductivity became so high that a resonance
type spectrum appeared with a negative dielectric constant at kHz
frequencies. It is likely that the downshift of the resonance frequency
with an increase in temperature has arisen from the increase in
conductivity.

[0028] Finally, an effect of dopant concentration on the negative
dielectric constant behavior was investigated. In the cases of PBI doped
with 50 or 60 wt % phosphoric acid measured at 300° C., the
dielectric constant increased with decreasing frequency at below
resonance frequency (shown in FIG. 3A). At low frequency, the dielectric
constant of the PBI doped with 60 wt % phosphoric acid was higher than
that of the PBI doped with 50 wt % phosphoric acid, which was expected
because of higher concentration of mobile ions. Also, the PBI doped with
60 wt % phosphoric acid showed a lower resonance frequency, fres and
a more negative dielectric constant at a lower frequency, fmin. Even
at room temperature, the 60 wt % doped PBI showed a negative dielectric
constant of -84.1 at 1.53×106 Hz. The 60 wt % doped PBI showed
a higher peak (max) conductivity (9.4×10-3 S/cm) at a lower
frequency, fmax (7.0×104 Hz) than the 50 wt % doped PBI
(4.9×10-3 S/cm at 1.0×105 Hz), which is related to
the negative dielectric constant behavior (show in FIG. 3B). It was found
that the effect of increasing concentration of phosphoric acid on the
negative dielectric constant was similar to that of increasing
temperature on the negative dielectric constant because of higher
mobility of ions.

[0029] Embodiments of the invention have at least the following
features/benefits: (1) the PBI doped with phosphoric acid displays a
negative dielectric constant due to the resonance behavior of the high
mobility of ions at high frequencies and elevated temperatures; (2) the
effective negative dielectric constant and resonance frequency can be
controlled by temperature, concentration and effective mass of dopant;
(3) the ion-doped materials of embodiments of the invention can be used
to create novel negative dielectric constant materials and negative index
materials; (4) the ion-doped materials of embodiments of the invention
can be used to create novel optical and microwave devices; and (5) the
ion-doped materials of embodiments of the invention can function as a
structural element and a medium for power generation and energy storage,
a sensor and/or an actuator.

[0030] The novel ion-doped negative dielectric materials of embodiments of
the invention provide a new method for preparing metamaterials (negative
index materials, NIM) with controllable resonance frequencies from radio
to optical frequency. Potential applications for the novel negative
dielectric materials of embodiments of the invention include, but are not
limited to, the following:

[0031] (1) Commercial Applications (including Aerospace Applications)

[0032] (a) Superlens (perfect lens): Conventional lenses have a resolution
on the order of one wavelength due to the so-called diffraction limit.
This limit makes it impossible to image very small objects, such as
individual atoms, which have sizes many times smaller than the wavelength
of visible light. A superlens is able to overcome the diffraction limit.
A very well-known superlens is the perfect lens described by John Pendry
(J. B. Pendry, Phys. Rev. Lett., 85, 3966 (2000); see also
http://en.wikipedia.org/wiki/Metamaterial;
http://en.wikipedia.org/wiki/Superlens), which uses a slab of material
with a negative index of refraction as a flat lens. In theory, Pendry's
perfect lens is capable of perfect focusing--meaning that it can
perfectly reproduce the electromagnetic field of the source plane at the
image plane. A superlens is a lens which is capable of subwavelength
imaging. Recently, experimental realizations of the superlens have been
achieved. The resolution capability was extended to 1/26 of the
illumination wavelength, providing unprecedented image details 15 nm and
below.

[0033] (b) Optical Power Limiting: NIM is applicable to make an optical
power limiting device providing protection of the human eye against
accidental or deliberate exposure to laser radiation for commercial and
military applications. The optical power limiting device utilizes planar
NIM layers for optical focusing and conventional nonlinear two-phonon
absorbing materials layers for limiting the optical power.

[0035] (d) Microwave and Related Applications: NIM materials make it
possible to achieve several applications that are not possible or would
be difficult without a magnetic response. For example, the new negative
dielectric material enables the production of "ultra thin film inductors"
which have unlimited applications for the integration of electronics to
pursue lightweight, flexibility, ultra small size and durability, in
comparison with general "bulk solenoid inductors". The new materials make
it possible to achieve several other applications such as waveguides and
antenna, filters, and electromagnetic cloaking devices. The inductance
and resonant frequency of the thin film inductors also can be tailorable
by controlling the doping level.

[0037] (f) Nondestructive Evaluation Technique: NIM material increases the
sensitivity of the microwave nondestructive evaluation method for
detection of defects that are small relative to a wavelength. Such a
sensor can be designed on the basis of a negative index material lens.

[0038] 2) Military Applications

[0039] (a) Cloaking (Stealth): NIM materials pave the way to conceptually
novel ways of making a given object "invisible" to electromagnetic
radiation, potentially overcoming some of the inherent limitations of
some camouflaging techniques. The mechanisms typically involve
surrounding the object to be cloaked with a shell which affects the
passage of light near it. Metamaterials have managed to cloak an object
in the microwave spectrum using special concentric rings; the microwaves
were barely affected by the presence of the cloaked object. Recently, a
metamaterial with a negative index of refraction for visible light
wavelengths was announced in the art. The material had an index of 0.6 at
780 nanometers.

[0040] (b) High-frequency battlefield communication: NIM materials make it
possible to make lightweight, flexible, ultra small size and durable
antennas applicable for wearable electronics such as multifunctional
military suits.

[0042] The corresponding structures, materials, acts, and equivalents of
all means or step plus function elements in the claims below are intended
to include any structure, material, or act for performing the function in
combination with other claimed elements as specifically claimed. The
description of the present invention has been presented for purposes of
illustration and description, but is not intended to be exhaustive or
limited to the invention in the form disclosed. Many modifications and
variations will be apparent to those of ordinary skill in the art without
departing from the scope and spirit of the invention. The embodiment was
chosen and described in order to best explain the principles of the
invention and the practical application, and to enable others of ordinary
skill in the art to understand the invention for various embodiments with
various modifications as are suited to the particular use contemplated.

Patent applications by Cheol Park, Yorktown, VA US

Patent applications by Jin Ho Kang, Newport News, VA US

Patent applications by Joycelyn S. Harrison, Arlington, VA US

Patent applications by Keith L. Gordon, Hampton, VA US

Patent applications by Peter T. Lillehei, Yorktown, VA US

Patent applications by USA as represented by the Administrator of the National Aeronautics & Space Administration